Price impact calculator

What it is telling you

A pool holds two reserves and multiplies them to a constant. Buy from it and you take tokens out, so the reserve you are buying goes down and the reserve you are paying with goes up. The price is the ratio between them, so the price moves while your own order is filling.

Price impact is the gap between the price you saw and the average price you actually got. It is not a fee anybody charges you and it is not slippage from someone front-running you. It is the cost of being the trade.

The arithmetic

Reserves start at x and y, and x·y = k never changes. Put Δx in and the pool must still satisfy k, so the tokens you get out are:

Work that through and almost everything cancels. The token reserve drops out, k drops out, and what is left is one division:

A 2 SOL order into a 40 SOL pool is 5%, and it is 5% whatever the token is, whatever the market cap says and whatever the chart looked like a second ago. On that order you give up 0.1 SOL before the token has moved a single percent on its own.

This is worth holding onto, because it means you can do the sum in your head at the moment it matters. If you are putting in a tenth of the pool, you are paying about ten percent. The calculator above is that division with the reserves drawn for you.

Why this hurts more on a launch

The formula is the same one Uniswap has used since v2. What changes on a memecoin is the size of x.

Every figure in that table is just the order over the pool, which is why it is exact rather than an estimate. A fresh pump.fun launch opens with reserves in the low tens of SOL. An order that would be invisible on a major pair is the whole move there, and you are paying the top you just made. Then you have to sell back through a pool your own buy has already reshaped.

• Impact is paid twice, once going in and once coming out.
• It scales with your size against the pool, not with your size in dollars.
• Splitting an order into smaller pieces genuinely reduces it, which is why the verdict above says to split rather than to skip.

Questions

Is price impact the same thing as slippage?

No, and conflating them costs people money. Price impact is what your own order does to the price, and it is knowable before you send anything. Slippage is what everybody else’s orders do between your click and your fill, and it is not knowable in advance. Your slippage tolerance protects you from the second one and does nothing about the first.

Does the unit matter?

No. Price impact is a ratio, so it comes out the same whether you put both numbers in as SOL, as dollars or as anything else, as long as the pool and the order are in the same unit. The sliders here say SOL because that is what a launch pool is quoted in.

Why is there no fee in the calculation?

Because the fee is a separate, smaller and much more predictable cost. The LP fee is a flat percentage you can add afterwards. Impact is the part that changes with your size, which is the part worth modelling.

Does a bigger pool always mean a better fill?

For the same order, yes, and the table above is monotonic for that reason. It says nothing about whether the token is worth buying, and a deep pool built to look deep is one of the older tricks on the surface.

Can I use this for the sell side?

The arithmetic is symmetric, so the same figure applies going out. In practice the sell is usually worse, because you are selling into a pool your own buy already moved.

Where the numbers come from

The same function that prices fills inside the Coinwar terminal, running here on numbers you set instead of on a live pool. Nothing is sent anywhere and nothing is stored. What the profitability data actually says is the other half of this.